1. Field of the Invention
The present invention relates to simple and efficient methods for producing L-fuculose and L-fucose.
2. Brief Description of the Related Art
L-Fucose (L-6-deoxygalactose) is ubiquitous throughout the living world, mostly as a non-reducing terminal sugar of various carbohydrates. For example, fucoidan in seaweed is a polysaccharide which contains L-fucose. L-Fucose is believed to be involved in the uptake of serum glycoprotein into the liver, and is able to induce receptors for macrophage migration inhibitory factor in vivo. L-Fucose has also been studied relative to its association with various diseases. For example, L-fucose has been studied as a pharmaceutical intermediate. Specifically, researchers are hoping to develop the ability to diagnose cancer based on the ratio of L-fucose in glycoprotein or glycolipid, or the change in the amount of free L-fucose in urine. Development of a cancer metastasis inhibitory agent and an antivirus agent with L-fucose is also anticipated. It is further anticipated to utilize L-fucose for controlling leukocytes and treating rheumatoid arthritis.
As described above, various applications of L-fucose are being developed for future use. However, methods for obtaining and producing L-fucose have already been developed. For example, methods for extracting fucoidan from Nemacystus decipiens (PJP S61-57520 A), and isolating L-fucose from fucoidan derived from Nemacystus decipiens have been described (JP H11-35591 A). However, a large amount of Nemacystus decipiens is required to perform these methods. In addition, it is difficult to isolate and purify the product with these methods, and the yield is small.
Isolation of L-fucose from a hydrolyzed polysaccharide produced by a microorganism has also been attempted and described (JP S59-51798 A). However, isolation and purification are also technically difficult using this method, and the yield again is also very small. A chemical synthesis method using D-galactose as a raw material has also been described (JP S61-57520 A); however, this method is not industrially practical because of the many steps which are necessary and the small yield.
As a synthetic method using an enzyme, converting L-fuculose-1-phosphate into L-fuculose using acid phosphatase and further converting into L-fucose using L-fucose isomerase has been described (International Publication WO97/15683 Pamphlet). However, L-fuculose-1-phosphate is expensive. Therefore, there is a demand in the art for a method which enables production at lower cost.
Oxidation of L-fucitol using NAD-dependent dehydrogenase derived from plants (Rhodophyta, red algae) has been reported (e.g., International Publication WO02/06506 Pamphlet; Planta 202: 487-493 (1997)). However, it is unclear which site of L-fucitol is oxidized, and the resulting products have not been definitely identified. In addition, it is generally difficult to produce an enzyme derived from a plant on a large scale for industrial applications, and thus, this method is inconvenient.
Furthermore, the oxidation of L-fucitol using acetobacterium has been reported (e.g., Journal of American Chemical Society; 4934-4937 (1950), Canadian Journal of Chemistry 45: 741-744 (1967)). However, no enzyme has been identified in these reports. The oxidation products are different depending on the oxidized site of L-fucitol. In these experimental reports, the major component of the resulting oxide has been reported to be not L-fucose or L-fuculose, but a substance resulting from oxidation at position 4 of L-fucitol (L-fuco-4-ketose in Journal of American Chemical Society; 4934-4937 (1950)). The acetobacterium has been extensively studied in relation to the enzyme acting on a sugar as a substrate (e.g., JP H8-242850 A, Canadian Journal of Chemistry 45: 741-744 (1967), Biosci. Biotechnol. Biochem. 65: 2755-2762 (2001)).
Although methods for utilizing L-fucose have been described, none of these methods are industrially available. Therefore, methods for producing L-fucose are desirable in the art, particularly for industrial use, and which provide ease of use and at a reasonable cost.